1. Field of the Invention
The present invention relates to a location registration area assigning method and a wireless communication system, and particularly to a signaling traffic reduction technique in which attention is paid to the separation between processes of location registration and handover.
2. Description of the Related Art
In order to use services such as mail and streaming video, a mobile device performs packet communication with a base station by wireless, and transmits and receives data for service to and from the Internet network through a gateway. When performing the packet communication with the base station, the mobile device may move between base stations. When the mobile device, which is located in a cell and performs the packet communication with the base station, moves to another cell, the mobile device and the base station perform a process called handover in order to continue the packet communication. The handover is disclosed in, for example, non-patent document 1. In the handover disclosed in non-patent document 1, the mobile device performs, in addition to the packet communication, signaling communication with a movement destination base station in order to change a packet communication destination from a movement origin cell to a movement destination cell. The packet communication and the signaling communication performed on a wireless section between the mobile device and the base station are performed on the same physical channel (physical shared channel). Since the packet communication and the signaling communication share the same physical shared channel, as the amount of signaling communication increases, the physical shared channel is congested and the data communication speed decreases.
Besides, when the mobile device performing the packet communication with the base station moves between cells, there is a case where not only the handover but also location registration is performed. The location registration is performed in order to notify a call processing control apparatus that the mobile device is located in which cell at present. The mobile device and the call processing control apparatus manage a paging area for informing an incoming call to the mobile device as a Tracking Area Identity list (TAI list). When a TAI of the movement destination cell is not included in the TAI list of the mobile device, the mobile device performs the location registration. The TAI is assigned to all cells, and is notified as notification information to the mobile device by the base station which manages the cell. The location registration using the TAI list is disclosed in, for example, non-patent document 2. Although the TAI list can be constructed of different combination of TAIs for plural mobile devices, since the number of TAIs which can be stored in the TAI list is 16, the combinations are limited. Thus, according to the combination of TAIs, plural user equipments (UE) perform location registration in the same cell.    Patent document 1: JP-A-2008-193261 (P2008-193261A)    Non-patent document 1: 3GPP (3rd generation partnerships) 3GPP TS 23.401 V9. 1.0    Non-patent document 2: 3GPP (3rd generation partnerships) 3GPP TS 24.301 V8.2.1
When a mobile device moves between cells when the packet communication is performed between the mobile device and the base station, not only the handover but also the location registration simultaneously occurs. The non-patent document 1 prescribes a process when the handover and the location registration simultaneously occur. In this case, since signaling communication due to the handover and the location registration occurs on the physical shared channel, the physical shared channel is more congested than in the case of signaling communication due to either one of them. Besides, when the handover and the location registration simultaneously occur since many mobile devices in a train or a bus move between cells, since a lot of signaling traffic occurs at a boundary between specific cells, the physical shared channel is further congested. When the physical shared channel is congested, the wireless state between the mobile device and the base station is congested, and the data communication speed is locally reduced.
As stated above, when plural mobile devices during data communication move between cells, the handover and the location registration can simultaneously occur in the movement destination cell. At this time, at a cell boundary, since a lot of signaling traffic occurs between the base station and the plural mobile devices, there is a problem that the physical shared channel is congested, and the data communication speed is locally reduced.